Doctrine\ODM\CouchDB\Id\IdGenerator::create PHP Method

    public static function create($generatorType)
    {
        switch ($generatorType) {
            case ClassMetadata::IDGENERATOR_ASSIGNED:
                $instance = new AssignedIdGenerator();
                break;
            case ClassMetadata::IDGENERATOR_UUID:
                $instance = new CouchUUIDGenerator();
                break;
            default:
                throw new \Exception("ID Generator does not exist!");
        }
        return $instance;
    }

 private function getIdGenerator($type)
 {
     if (!isset($this->idGenerators[$type])) {
         $this->idGenerators[$type] = Id\IdGenerator::create($type);
     }
     return $this->idGenerators[$type];
 }